The present invention relates to a process of copper recovery using an ion exchange resin, and more particularly one which will allow 100% recovery of copper from an acid process stream while neither utilizing more than negligible water uptake nor producing any water borne metal laden waste, by stoichiometrically balancing the water between the absorption, elution and wash. The invention also can also be utilized to increase the recovery of copper and other metals such as zinc and nickel in existing process environments.
In terms of the history of copper recovery generally, in the late 1960s and into the 1970s began the rise of a process called SX-EW (Solvent Extraction Electro-Winning) for the recovery of copper from soluble copper ore leachates. This technique has evolved to permit recovery of copper, of London Metal Exchange grade, from large heap leach operations producing copper pregnant leach solutions (PLS) in the range of 1-6 grams of copper in a liter of PLS. The economics of the SX process, since it is based upon an equilibrium, favor the use of higher solution grades as a copper input stream. When solution copper levels drop below 1 gram per liter SX economics become distinctively less attractive.
One reason that the investment and operating economics deteriorate with lower PLS grades results from the inherent design of the SX systems. The size of the SX plant is a function of the phase disengagement rates between the solvent and the aqueous liquids. This size is therefore a function of volumetric flow rate and is limited in its efficiency by the liquid contact and mixing, among other factors. In contrast, the size of an IX system is directly related to the kinetics of adsorption and de-sorption of the copper species and therefore is a function of the mass flow of copper production.
Further, because the SX operation has a system which depends upon a limited number (typically one or two) of equilibrium extraction stages and fails to have the potential to remove 100% of the copper, the scale of SX must tend to be large in order to be economic and the SX operation will always produce loss of copper in a waste stream. Depending upon where the copper recovery operation occurs, hazardous waste necessarily is created. CIX in contrast has many stages in which equivalent equilibrium contact in a short length of resin bed and can be easily configured to reduce copper in the bed effluent to very low levels to obtain high recoveries in a single operation.
Despite the inherent advantage of CIX in terms of extraction efficiency, conventional continuous ion exchange (CIX) still suffers several major obstacles, and a discussion and illustration of these problems will be aided by a discussion of the state of the art of aspects of the best known CIX system. Although the processes described in the prior art and the invention will be couched in terms of copper generally, the overall process can be used with other metals which are subject to being treated with the same processes. In terms of an overall mine process, crushed ore is contacted with an acidic aqueous solution which causes the copper in the ore to form a soluble copper solution. The soluble, acidic aqueous copper solution is allowed to contact an ion exchange resin, commonly reported in the literature as XFS 4195/4196/43084 which is commercially available from DOW Chemical Company, Liquid Separations, P.O. Box 1206 Midland, Mich. 46842-1206 under the DOWEX trademark. The geometry into which these resin ion exchange materials are placed can vary widely based upon the expected flow rates, regeneration requirements (both timing and flow).
Details of the operation of the above resins are given in a paper entitled “Copper Selective Ion Exchange Resin with Improved Iron Rejection”, Journal of Metals Vol 31, No 3, 1979, R. R. Grinstead, Dow Chemical USA.
The performance of the resins are given in an article entitled “Copper Recovery from Leach Liquors using Continuous Ion Exchange”, Randol Conference, Vancouver 1998, Rossiter, Gordon J.; Carey, Kenneth C. As described therein, one of the peculiarities of utilizing a column of the types described above is the column's affinity for trapping iron, if only momentarily, before the column is fully selectively loaded with copper. As a result, the basic column operation includes loading with a copper stream (which may contain iron), while (1) fully loading the bed with a pure copper stream to displace any iron which may have been attracted onto sites not fully saturated with copper, or (2) possibly introducing a dilute acid stream dosed with SO2 to remove impurities and reduce any Fe3+ to Fe2+, the latter ionic species having a lesser affinity for the resin sites.
Since the Fe is displaced by the copper during a column's normal activity, any residual Fe buildup is at the downstream flow site and so the scrub process is accomplished with flow in the same direction as that in which copper absorption operation occurred. The scrub reduces the residual Fe on the resin to a lesser percentage of the total Fe which was originally absorbed along with the copper.
The beginning of the copper stripping step also quickly elutes the remaining Fe (the lesser percentage) still present on the resin after the scrub operation into the first volume of stripping electrolyte used. Only a small amount of copper is lost in this first volume of stripping electrolyte and the remainder of the stripping electrolyte essentially completely removes the remainder of the copper. Stripping uses 70-200 grams per liter H2SO4, can be done with one bed void volume but is more complete with two.
The overall process described includes a copper/iron feed inlet stream (PLS), a depleted copper/iron raffinate exit stream, a spent electrolyte inlet stream which is a adequate to absorb copper during stripping, and the strong electrolyte exit stream carrying the copper product from the stripped column.
However, the Rossiter system proposed in the 1998 paper proposed a continuous scheme yet failed to solve the issue of the water balance, complete copper recovery and closed loop operation clearly.
In a summary of the state of the art for copper extraction from leach solutions, Alan A. Taylor, in his article entitled “Copper SX/EW Any Rivals in Sight Alta Metallurgical Services”, February 2002”, mentions the potential of IX for the future but only considers IX as a pre-concentration technique to boost the concentration of the process stream.
Jones and Pyper along with Grinstead of Dow Chemical worked in the 1970s and early 1980s developing resin based materials and IX techniques for copper recovery. A number of publications resulted, including “Recovery of Non-Ferrous Metals from Acidic liquors with a Chelate Exchange Resin in the Presence of Iron(III)”, U.S. Pat. No. 3,998,924, Dec. 21, 1976, Jones, Kenneth C. and Wheaton, Robert M.; “Copper Recovery from Acidic Leach Liquors by Continuous ion-Exchange and Electrowinning”, Journal of Metals, Vol 31. No. 4, April 1979, pp. 19-25, Jones, Kenneth C., Pyper, Randall A.; and “Extraction of Copper, Nickel and Cobalt using Alkyl Aromatic Sulfonic Acids and Chelating Amines”, U.S. Pat. No. 4,254,087, Mar. 3, 1981, Grinstead, Robert R.
Since then there has been little commercial effort to implement IX as a primary process for concentrating and purifying copper from leach solutions.
In summary existing technology still faces major obstacles to an effective, economic and environmentally friendly process using CIX (Continuous Ion Exchange) for copper recovery from leach solution. The main problem areas which have yet to be solved include:                                    (1) Water availability and consumption associated with resin wash/scrub and rinsing operations. Problems in the water balance drive other problems and include (a) a build-up in water used for the leaching operation causes excess use of acid and a resulting disadvantageous dilution of copper leach concentration (which can be a severe problem in areas where rainfall is an issue in maintaining a volume balance around the leach circuit); (b) the need for extra evaporation equipment to remove the excess water from the leaching operation circuit; (c) excess water in the electrolyte which necessitates an excessive bleed of electrolyte and resulting copper and other electrolyte component losses and (d) the expense involved in generating wash/rinse waters in desert climates and the cost of treating such waters to remove undesirable mineral impurities;                        (2) Inability to hold a constant volume balance in the resin elution electro-winning circuit;        (3) Maintaining a Cu:Fe ratio of metals (purity) transferred into the electrolyte similar to that obtained by SX processes;        (4) Overcoming the costs associated with maintaining a large inventory volume of resin; and        (5) Unfavorable economics associated with the use of other chemicals and chemical systems to reduce feed iron levels.        
What is needed is an invention which can overcome the above limitations and shortcomings to enable control and recovery of all the copper, combined with a more environmentally friendly mode of operation. The needed system should be compatible with a multi-port valve CIX system in order to facilitate automatic operation and monitoring. The needed system should be compatible with commercially available membrane technology (nano-filtration) and iron reduction techniques to solve the above problems.